In a film stack of bathocuproine (BCP) (electron transport layer), fac-tris(2-phenylpyridyl) iridium(III) [Ir(ppy)(3)] blended in 4,4'-bis(N-carbazolyl) biphenyl (CBP) (light-emitting layer), and 4,4',4 ''-tris(N -carbazolyl) triphenylamine (TCTA) (hole transport layer), the BCP and Ir(ppy) 3: CBP layers rapidly interdiffuse by anomalous Fickian diffusion. Diffusion leads to a decrease of up to 33% in the solid-state emission but no change in color.